How can I make flaky edges for cinnamon stick?
I separated the Object Data so I could modify each model independently.

The model on the left has the Solidify Modifier Applied since it restricts Vertex Painting and UV Mapping, (I wanted to try a few things there.) 

The model on the right is mostly the same as you made it.  

I used Vertex Paint and a Particle System on both of them.

There is a Group of several jagged models on a hidden layer that are being used to simulate the flecks along the edges. 

It's really now just a matter of cloning those pieces using the particle system and using weight painting to control the distribution on the cinnamon stick models.

To make a series of Objects connected using a Group, press g while in Object mode after you have selected all the Objects for the group.  They should now all be highlighted in green.  I find this works best when you have the Objects facing down the y-axis with the Origin at (0,0,0).  I also, prefer to rotate them in Edit mode to avoid having to apply the rotations.



In the Particle's Render tab, activate the Group option and Select the group.  It would be better to change the name 'group' to something more like 'flecks' since Blender also calls Vertex Groups 'group' and since Weight Painting adds a Vertex Group, this can be confusing.

Also, in the Particles tab, add 'Group' to the Vertex Group's Density
field.  Now any weight painting that you've done on the model should control where the flecks show up.  Adding the Vertex Group control to the Length helps here as well.





Here's the modified .blend file.